Fischer-Tropsch synthesis for the catalytic production of hydrocarbons from synthesis gas, i.e., carbon monoxide and hydrogen, is well known in the technical and patent literature. Similarly, the technology needed to convert natural gas or methane into synthesis gas is also well established. In like manner the conversion of methanol into high quality transportation fuels particularly middle distillate fractions, is also a well recognized technology.
The first commercial Fischer-Tropsch operation utilized a cobalt catalyst, though later iron catalysts were commercialized. The use of nickel-thoria on kieselguhr as a Fischer-Tropsch catalyst was an important advance in this field of catalysis. Additional developments led to more advanced cobalt catalysts comprising cobalt and thoria on kieselguhr, and cobalt-thoria - magnesia on kieselguhr.
In general the Group VIII non-noble metals, iron, cobalt and nickel have been widely used in Fischer-Tropsch reactions, these metals being promoted with various promoters and supported on a variety of supports.
Recently great strides have been made in catalysts for the conversion of synthesis gas, methanol and/or natural gas or methane into hydrocarbons suitable as transportation fuels or other high value products such as lubricants or specialty oils or waxes.
Examples of such advanced catalysts include particulate catalysts comprising cobalt or cobalt and thoria on titania or titania-containing supports, preferably a titania support having a rutile:anatase content of at least about 2:3, as determined in accordance with ASTM D 3720-78:Standard Test Method for Ratio of Anatase to Rutile in Titanium Dioxide Pigments By Use of X-Ray Diffraction. Additional examples of advanced cobalt catalyst include those comprising cobalt promoted with zirconium, hafnium, cerium or uranium and cobalt or cobalt and thoria promoted with rhenium deposited on inorganic oxides of Group III, IV, V, VI and VIII of the Periodic Table of Elements, preferably titania.
The mode of deactivation of such hydrocarbon synthesis catalysts is not too well understood, but is believed to be related, at least somewhat, to the mode in which the hydrocarbon synthesis is carried out; e.g., a different deactivation mode is likely present for catalyst in fixed bed operations than the deactivation mode for slurry phase operations. Thus, fixed bed processes are essentially plug flow operations involving reactant gradients as they progress through the catalyst bed whereas slurry phase operations involve sufficient backmixing tending towards a more uniform distribution of reactants and products throughout the slurry phase. For example, in a fixed bed water would not be present at the start of the reaction and would build up as the reaction progressed through the bed. However, in a slurry phase, e.g., in a slurry bubble column, because of backmixing effects, water will be present throughout the reaction slurry bed. Consequently, deactivation modes, dependent to any degree on the presence of water, will be different for fixed bed and slurry phase processes.
Reactivation - rejuvenation of such deactivated catalyst has been a pressing need in any consideration given to the commercialization of a hydrocarbon synthesis process.
Reactivation - regeneration involving air or oxygen burning of the catalyst to remove the deactivation moieties present on the catalyst followed by a hydrogen reactivation step has been a delicate process which is not always successful.
Similarly, hydrogen rejuvenation treatments have been employed with catalysts operated in fixed beds with, at best, limited and inconsistent recovery of hydrocarbon synthesis activity. In one case, steady state operation in the fixed bed had not been achieved, in other cases excessively high temperatures were employed, and still in other cases the hydrogen treatment was in the absence or substantial absence of hydrocarbon liquids. The development of a simple, reproducible reactivation - regeneration process and attendant hardware for treating deactivated hydrocarbon synthesis process catalyst would greatly contribute to the commercialization and success of hydrocarbon synthesis.